1. Field of the Invention
The exemplary embodiments described herein relate to power amplifier linearization through digital predistortion, and a method for linearizing power amplifiers having memory effects.
2. Background of the Invention
Power amplifiers (PAs) are the main cause of nonlinearities in transmitters used in communication systems. These nonlinearities appear as a result of using spectrum efficient modulating techniques which lead to amplitude modulated time domain signals with high peak-to-average power ratios (PAPR). The signal's amplitude modulation emulates the static nonlinear behaviour of PAs. Moreover, electrical memory effects will be induced due to the wide bandwidth of these signals. In order to meet the spectrum emission requirements of modern communication standards, digital predistortion is needed to compensate for the nonlinearity of power amplifiers. As a result, an accurate predistorter that compensates for both dynamic and static behaviours of PAs is needed for communication and broadcasting applications.
Static nonlinear behaviour appears as a deviation of the gain from its constant value as the instantaneous input power approaches the saturation region in the AM/AM and AM/PM characteristics of the PA, while dynamic behaviour appears as dispersion in these same characteristics (F. M. Ghannouchi and O. Hammi, “Behavioral modeling and predistortion,” IEEE Microw. Mag., vol. 10, no. 7, pp. 52-64, December 2009—incorporated herein by reference). For power amplifiers exhibiting memory effects, many behavioural models and digital predistortion functions have been proposed (F. M. Ghannouchi and O. Hammi, “Behavioral modeling and predistortion,” IEEE Microw. Mag., vol. 10, no. 7, pp. 52-64, December 2009—incorporated herein by reference), (Y. J. Liu, J. Zhou, W. Chen, B. Zhou, and F. M. Ghannouchi, “Low-complexity 2D behavioural model for concurrent dual-band power amplifiers,” Electronics Letters, vol. 48, no. 11, pp. 620-621, May 2012—incorporated herein by reference), (J. Kim and K. Konstantinou, “Digital predistortion of wideband signals based on power amplifier model with memory,” Electronics Lett., vol. 37, no. 23, pp. 1417-1418, November 2001—incorporated herein by reference), (D. R. Morgan, Z. Ma, J. Kim, M. G. Zierdt, and J. Pastalan, “A Generalized Memory Polynomial Model for Digital Predistortion of RF Power Amplifiers,” IEEE Trans. Signal Process., vol. 54, no. 10, pp. 3852-3860, October 2006—incorporated herein by reference), (R. Raich, H. Qian, and G. T. Zhou, “Orthogonal polynomials for power amplifier modeling and predistorter design,” IEEE Trans. Veh. Technol., vol. 53, no. 5, pp. 1468-1479, September 2004—incorporated herein by reference), and (O. Hammi, F. M. Ghannouchi, and B. Vassilakis, “A compact envelope-memory polynomial for RF transmitters modeling with application to baseband and RF-digital predistortion,” IEEE Microw. Wireless Compon. Lett., vol. 18, no. 5, May 2008, pp. 359-361—incorporated herein by reference). Due to its ease of use and acceptable performance, the memory polynomial (MP) model (see J. Kim and K. Konstantinou, “Digital predistortion of wideband signals based on power amplifier model with memory,” Electronics Lett., vol. 37, no. 23, pp. 1417-1418, November 2001—incorporated herein by reference) has been an appealing one. Later several of its variants were reported in the literature (D. R. Morgan, Z. Ma, J. Kim, M. G. Zierdt, and J. Pastalan, “A Generalized Memory Polynomial Model for Digital Predistortion of RF Power Amplifiers,” IEEE Trans. Signal Process., vol. 54, no. 10, pp. 3852-3860, October 2006.—incorporated herein by reference), (R. Raich, H. Qian, and G. T. Zhou, “Orthogonal polynomials for power amplifier modeling and predistorter design,” IEEE Trans. Veh. Technol., vol. 53, no. 5, pp. 1468-1479, September 2004—incorporated herein by reference), and (O. Hammi, F. M. Ghannouchi, and B. Vassilakis, “A compact envelope-memory polynomial for RF transmitters modeling with application to baseband and RF-digital predistortion,” IEEE Microw. Wireless Compon. Lett., vol. 18, no. 5, May 2008, pp. 359-361.—incorporated herein by reference).